Transfer system for electric circuits



Nov. 9, 1954 B. w. BATES TRANSFER SYSTEM RoR ELECTRIC CIRCUITS Filed Aug. ll, 1952 @SW u q] 'fihi United States Patent O TRANSFER SYSTEM FR ELECTRIC CIRCUITS Byron W. Bates, Seattle, Wash., assignor to Boeing Airplane Company, Seattle, Wash., a corporation of Delaware Application August 11, 1952, Serial No. 303,753

Claims. (Cl. 307-64) This invention relates to automatic change-over sys-V tems by which, among other operations performed, a failure of the power supply or other normally operative unit in one section of the system causes that unit to be disconnected from the system and a spare unit to be substituted in its place, and if there happens to be a failure in more than one section of the system at the same time then the substitute unit will automatically replace the unit which is of greatest importance or highest priority in carrying out the functions of the over-all system. The invention is herein illustratively described by reference to the preferred form thereof as applied to an airplane electric power distribution system having a plurality of inverters supplying direct current to a corresponding number of separate busses which feed individual loads of varying importance to the airplanes operation. However, it will be appreciated that certain changes and modifications departing from the specific illustration may be made while remaining within the scope and purposes of the invention as herein disclosed.

ln brief, the electrical system involved in the illustration employs inverters for converting direct current into alternating current and, through busses, supplying the latter to a variety of different airplane components. These components are classified in a certain consecutive order of priority to receive electrical power in the event there is an insuicient supply for all, caused, for instance, by failure of one of the inverters. ln the illustration there are four such groups or classes, although the number may vary in different applications of the invention without changing the principles of operation involved. The rst group of the four mentioned in the` example, in order of priority, is termed the main group, consisting of those components, such as ight instruments and other vital devices of highest relative importance to the airplanes operation. The group or type second in priority in the particular illustration is referred to as the No. l camera, and the group of third highest importance, the No. 2 camera. Of lowest importance and priority is the group herein termed the secondary" group, comprising one or more components which are least necessary and would be the first to be dropped out of operation in an emergency. ln carrying out the invention the electric power distribution system is sectionalized, such that each class of components is separately energized by its individual inverter and associated D.C. bus. In addition, a spare inverter is provided.

ln the operation of the system this spare inverter is substituted automatically for any one of the four inverters mentioned when any of them fails, and, as a highly important feature, the control circuits eifecting the substitution are so constituted that the spare inverter always replaces the inverter of highest priority among all that have failed regardless of whether or not the spare is already substituting for another inverter of lower priority. In achieving this result, the system comprises separate change-over or transfer relays associated with the respective inverters. When the relay of one inverter is actuated to elect a change-over connection, a disabling means associated with that inverter is also actuated, and prevents subsequent actuation of the transfer relays of all lower priority inverters. Preferably these disabling means comprise switches interposed in common energizing circuit conductors for the different transfer relays, as will be more fully described hereinafter.

Moreover, the secondary inverter (that of lowest priority) may be switched by manual control into the CJI ICC

place of the main inverter when the latter fails, and the spare will then automatically substitute for the secondary, but as a result of the automatic action just described the spare is still available as an automatic substitute for either of the two camera inverters should either of them fail.

Provision is also made for switching the spare inverter by manual control to substitute for any of the normally operative inverters, and in this case the priority sequence connections of the system insure that the spare may always be substituted manually for an inverter of higher priority than one for which it happens to be substituting, at the time of change-over. That is, the manual changeover controls for switching from any inverter to the spare effectively override the similar controls of lower priority inverters.

As an incidental feature, auxiliary control means in the system furnish over-voltage protection for the bus being supplied by either the secondary inverter or the spare inverter, when either of such inverters is substituting for the inverter normally supplying that bus, and when the normal over-Voltage protection apparatus of that bus is therefore ineffectual. Provision is also made for optionally nullifying the elfect of this auxiliary overvoltage protection apparatus when desirable, as when operating under conditions wherein no other source of power is available than the substituted spare or secondary inverter, for a particular bus, and it is more important to have a faulty supply of power available for that bus than no supply of power at all.

Furthermore, provision is made insuring against the possibility of parallel operation of a failed inverter and a substitute inverter on the same bus, such provision including a transfer relay which has one set of contacts operable to disconnect the failed converter from the bus and another set operable simultaneously to connect the substitute inverter to the same bus, said two sets of contacts being mechanically interconnected so that they cannot fail to operate except together. Moreover, the two sets of contacts are located immediately adjacent the bus in a physical sense so that the connections between the contacts and the bus will be as short as possible and thereby normally isolate the bus from the sometimes long feed conductors extending therefrom to remotely located inverters. Thus the individual sections of apparatus associated with the diterent busses are rendered less vulnerable to bus grounding hence loss of a section of components, due to bullets or shrapnel, for example, than they would otherwise be.

Another advantage of the disclosed priority changeover system lies in its application without regard to the number of sections each with an inverter and associated bus. Sections may be added to a basic system without disturbing the existing circuit connections appreciably, especially if the added inverters are to have successively lower priority than the existing inverters. Little revision in the connections is necessary even in modifications wherein the priorities are to be changed around.

While systems have previously been available for switching between a normal power supply and a spare power supply, without regard to the possibility of substituting a secondary power supply for the normal power supply by separate switching action, such systems, particularly the one replaced by the present system, have lacked priority type switching arrangements, and have involved an unduly large number of relays and circuit breakers, which add to the weight and bulk of the apparatus. Moreover, the former system afforded no protection against the parallelism of inverters, one a failed inverter, on the same bus, which would result in the substitute inverter acting as a power source driving the other inverter as a motor with attendant loss of electrical power. The former system also presented certain other difficulties such as the possibility of indelinite cycling in the control switches causing the normal inverter and the spare inverter to be started and stopped repeatedly in alternate fashion, with attending high surge currents, if neither failed to operate normally. An incidental disadvantage of the former system replaced by the present system was the necessity of rst starting the main inverter, for example, before it was possible `to replace it with the secondary inverter. These difficulties and others of the former system have been overcome in the present system.

The foregoing and other features, objects and advantages of the improved transfervsystem for electric circuits will become more fully evident from the following description by reference to the accompanying drawing.

The drawing constitutes a schematic circuit diagram of the illustrative power circuit for airplanes embodying the selective transfer system of the present invention.

In order to simplify the circuit diagram and enable visualizing the various circuit operations more readily, the common expedient of separating relay contacts from their associatedv relay coils in the diagram is adopted. For instance, all those contactsbearing the respective notations TR or TD with a certain prefix number, for example, correspond physically to the relay coils having the same notations and prefix number. Thus the one relay 32TD has a field coil of the same designation and tour sets of contacts, designated SZZTDl, 32TD2, 32DT3 and 32TD4 located at different points in the diagram. A similar scheme of notation also applies to the other relays.

Referring to the diagram, there are four normally operative inverters, the main inverter 1t), the No. l camera inverter i2, the No. 2 camera inverter i4, and the sec'- ondary inverter 16. There is also a spare inverter I8, which is normally inoperative. Each of these tive inverters is` placed into operation by the application of D.C. voltage to its switch terminals labeled SW in conventional fashion. In an airplane system of modern design this voltage is 28 volts D.C. Application of D.C. voltage to the main inverter 10 occurs by moving the gang switch 2t) into its right-hand position labeled N, and doing likewise with gang switch'22, thereby forming a circuit initiating operation of that inverter' extending from D.C. source terminal 24, and through conductor 26, switch arm 22L, conductor 28, switch arm ZtPL, conductor 30, the normally closed contacts 32TDI of relay 32TD, conductor 34, switch arm 20R, conductor 36, and conductor38 to an internal contactor'coil (not shown) of a conventional nature within the inverter, and then to a ground connection (not shown). When that circuit is formed and the contacter coil energized the latter effects closure of an inverter motor energizing circuit drawn only in part as extending from D.C. terminal 40 to one of the SW terminals of the inverter.

In like manner the No. l camera inverter may be started when its control coil (not shown) is energized with D.-C. voltageapplied through the circuits extending from the D.C. terminal 42, conductor 44, the middle arm 6L of switch 46 in the N position of such switch, conductor 4S, the normally closed contacts SilTDin of relay Sli-TD, conductor 52, gang switch arm 461%, conductor 54, and conductor 56, to the control coil and then to ground. Inverter motor current is then established from terminal 58 of the D.-C. energy supply source as in the previous instance.

Operation of No. 2 camera inverter 14 is similarly initiated through the control circuit extending from D.-C. terminal 60, throughconductor 62, switch arm 64L of gangswitchfi Vin itsv N (normal) position, conductor 66, the normally closedcontacts 68TD4 of relay 68TD, conductor 7G, switch arm 64R,l conductor '72, and conductor 74 to the control coil inside the inverter and then to ground. Terminal 76 of the D.C. energy supply source is connected to Ythe inverter motor by energization of such control coil (not shown).

Secondary inverter 16 is operated by completion of the control circuit extending from D.-C. terminal 78 and through conductor 80, the arm SZL of relay 82 in its N position, conductor 84, the normally closed contacts TDlof relay 86TD, conductorSS, switch arm 82B, conductor S4, and conductor 86, to the inverter control coill (not shown) andthen to ground. Terminall S8 of the D.-C. energy supply source is connected to the inverter. motor asin the preceding instance.

The circuit connections andconductors for energizing the spare inverter 1 8 will be, described subsequently. Normally this inverter is deenergized asnpreviously menf tioned.

Energization of the four normallyY operated inverters,

'10, '12, 14 and lfprodu'ces'AFC;A voltage across the inverter terminals designated A.C., and this voltage is applied to theirv respective load busses. 99,. 92,94 and1-96 for distribution to the various components (not shown) involved in operating the particular airplane and its related equipment. The bus is connected to the A.C. 'terminals of main inverter 10 through the normally closed contacts 98TR2 of transfer relay 98TR, and the normally closed contacts 100SM1 of relay lltltlSM (upper right of diagram). V`A. C. voltage from.' the No.l camera inverter 12 is applied to bus 92 through the normally closed contacts 102TR2 of transfer relay HPZTR; Similarly, A.C'. voltage from the No. 2 camera inverter 14 is applied to the bus 94 through the normally closed contacts MMTRZ of transfer relay MMTR. The bus 9b' receives A.C. voltage from secondary inverter 16 through the normally closed contacts` 1,06TR2 of transfer relay ltlTR, and the normally closed contacts ltiSMS of relay ltltlSM previously mentioned.

The A.C. voltage from spare inverter i8, when that inverter is energized, is available to all the four busses from feed conductor 108l having a circuit breaker il() therein to protect the spareY inverter. The conductor iti?. extends to the physical location ofeach bus, although is normally disconnected therefrorn. The nor,-

`mally opened TR relay contacts 98TR1, 102TR1, llliTRl and 106TR1, are provided to connect the feed conductor 39S to the respective busses 90, 92, 94 and 96m selective manner as later described.

A desirable feature of construction of the system is the physical location of the TR relays immediately adjacent the busses with which their respective contacts are operatively associated. Normally these busses are located behind spars or other protective structural ele. ments of an airplane where they are less vulnerable to battle damage, and they are therefore located remotely from the inverters which supply them with energy. As` a result, long feed conductors are necessary from the inverters to the busses. If the relay contacts for switching these busses on and oif their respective supply inverters were located at the inverter ends of vthe feed conductors instead of at the bus ends of such conductors, then the busses would be elfectively extended in length, and the extensions would not be as easily shielded be.- hind spars and other. structural elements as are. the busses. Thus the possibility of grounding of the feed conductors due to battle damage in that event would constitute a corresponding hazard to the operation of components connected to the bus. Consequently the TR relay contacts mentioned are placed in the immediate vicinity of the respectiveA busses which they serve in switching between different feed conductors to energize such busses.

Another incidental but important feature relating. to the TR relays is the provision of a mechanical connection or interlock between the two sets of contacts, namely the contacts TR1 and TR2, of each TR relay, so thatv when one set of contacts shifts-position, the other sety is. necessarily caused to shiftin the opposite sense. As a, result there isA no possibility of connecting thespare` inverter feed conductor 10S. through the associated TRI contact to a bus at the same time that bus is` also connected to its normal inverter through the corresponding TR2 contact. This avoids the loss of power and otherl hazards of having two inverters, one a possibly damaged inverter whichv has failed, operating in parallel,'such thatthe spare inverter v drives the other inverterV as. an A.C. motor.

In order to effect a substitution of the spare inverter 18 for either of the four nomally operative inverters, it is necessary in the operation of the systemA to perform three operations, first energize the spare inverter, secondly, disconnect the normally operative inverter Vfrom its bus, and, thirdly, connect the spare LinverterV A.C; feed conductor 2108 to that bus. These operations need not occur necessarily in the order enumerated. There are two available ways in thefsystem to accomplish the,V change-over, one being byv manual control exercised through selective operation of the respective gang switches 20, 46, 64, or 82, and the other being Aby automatic operation, initiated, for examplefbyfailure of an inverter causing an over-voltage or under-voltage condition on its bus. Both avenues of controlling thesubstitution of the spare inverter vfor any of the. other inverters involve the energivzation of the yTR relayassociatedwith the failed inverter. The manual-method' of effecting the! substitution will be discussed first, and then the automatic method. I

In order to substitute spare inverter 18 for main inverter 10, for example, by manual control, the gang switch 20 is moved to its left-hand position designated S. This applies the D.C. voltage of conductor 28 to the coil of relay 98TR, through switch arm 20L and conductor 112, and thereby effects opening of relay contacts 98TR2 and simultaneous closing of relay contacts 98TR1, to disconnect the main inverter from bus 90 and connect the spare inverter 18 to that bus. While the foregoing takes place the D.C. voltage of conductor 28 is also applied through switch arm M and conductor 114 to the SW terminals of the spare inverter to place that inverter in operation as desired.

In similar fashion it is possible to substitute the spare inverter by manual control for any of the other inverters. In the case of the secondary inverter 16, this is accomplished by shifting the gang switch 82 to its left-hand position designated 8. When that takes place, the D.C. voltage of conductor 80 is applied to the SW terminals of the spare inverter through the switch arm 82M, conductor 116 and conductor 114. At the same time this voltage is also applied by switch arm 82L to the coil of relay 106TR through conductor 118 to effect reversal in the positions of relay contacts 106TR1 and 106TR2, and thereby connect feed conductor 108 to bus 96 and disconnect that bus from the secondary inverter 16. In like manner shifting of the gang switches 46 or 64 to their S positions effects substitution of the spare inverter for the inverters 12 or 14, respectively. As will later appear herein, the switch 20 has overriding effect on switches 46, 64 and 82 for that purpose, as does switch 46 over switches 64 and 82, and as does switch 64 over switch 82, due to the action of certain disabling switches (i. e. relay contacts 32TD3, 50TD3 and 68TD3).

It is also possible by manual control to substitute the secondary inverter 16 for the main inverter 10, although there is no provision for automatically doing this, nor is there provision in the example for substituting the secondary for either the No. l camera or No. 2 camera inverters.

In order to accomplish the substitution of the secondary for the main inverter, by manual control, gang switch 22 is shifted to its left-hand position, designated S, which applies the D.C. voltage of conductor 80 to the SW terminals of the secondary inverter through the switch arm 22R, conductor 120 and conductor 84. This switching action also applies the DfC. voltage of conductor 26 to the coil of relay 100SM, through switch arm 22L, and when this relay is energized it opens its contacts 100SM1 (lower left) to disconnect the main inverter 10 from the bus 90 and simultaneously opens its 100SM3 contacts to disconnect the secondary inverter 16 from its normal bus 96, while closing the 100SM2 contacts to connect the secondary inverter to the bus 90 through feed conductor 122. Thus the main inverter 10 has available to it the secondary inverter 16 as one possible substitute, and as later described, the main inverter also has available to it, as do the remaining three normally operative inverters, the possibility of automatic or manual substitution of the spare inverter 18 therefor in the event of a failure of the particular inverter.

As previously mentioned, the system also provides for the automatic substitution of the spare inverter 18 for any of the four other inverters when an under-voltage or an over-voltage condition develops on the bus of a particular inverter. The circuit components and connections by which these results are accomplished will now be described.

The over-voltage and under-voltage sensing elements in the illustrative case are energized by D.C. voltage. To this end the bridge-connected rectitiers 124, 126, 128 and 130, are connected to the respective busses 90, 92, 94 and 96. The coils 132UV, 134UV, 136UV and 138UV are connected across the output potential points of the respective rectifiers and have variable compensating or adjusting resistors (not labeled) in series with them in order to establish their drop-out voltages at the desired values. Similarly, the over-voltage relay coils 140OV, 142OV, 144OV and 146OV are likewise con nected across the output potential points of the respective rectifers, each such coil having a variable compensating or adjusting resistor by which the actuating voltage of the relay energizing circuit may be established and adjusted to the desired value. A condenser C connected across each such over-voltage relay coil prevents tripping of such relays due to momentary circuit transients which do not represent a fault condition. Preferably all over-voltage relays used in the system are of the inverse time-voltage type.

The contacts 132UV1 of under-voltage relay 132UV are interposed in conductor 148 between the normally energized conductor 34 and the heater element 150H of a thermally actuated switch having contacts 1501-11 connected between conductors 30 and 112. Under normal operating conditions contacts 132UV1 are open, so that the heater element 150H is deenergized and its associated contacts 150H1 are open. The over-voltage relay OV has a set of contacts 152OV1 which are likewise connected between conductors 30 and 112, and these contacts are also normally open. In addition, the contacts 32TD1 of relay 32TD are also connected between conductors 30 and 112, and these likewise are normally open. It will be apparent that closure for any reason of either of these three sets of contacts, namely H1, 32TD1 or 152OV1, will apply the D.C. voltage on conductor 30 to the coil of relay 9STR through conductor 112.

The same possibility exists in connection with the section of system associated with the No. l camera inverter 12, and likewise those sections associated with the No. 2 camera inverter 16 and the secondary inverter 16, respectively. Thus the sets of contacts 134UV1, 136UV1, and 138UV1 of the respective inverter sections are adapted to apply D.C. voltage from the respective normally energized conductors S2` 70 and 88 to the respective heating elements 154H, 1561i and ISSH of thermally actuated switches having contacts H1 bearing corresponding prefix numerals in the diagram. The heater switch contacts 1541-11, 156111 and 158H1, normally open, are connected between conductors in the respective inverter surface sections ismilar to conductors in the section of circuit already described in connection with the main inverter 10, and to the same effect with respect to the energization of the respective TR relay coils 102TR, 104TR and 106TR.

In addition, the relays 32TD, SGTD, 68TD and 86TD have correspondingly numbered contacts TD2, which are interposed in the conductors interconnecting the spare inverter energization conductor 114 with the N con tacts of the middle switch arms 20M, 46M, 64M, and 82M of the respective manual cntrol switches, so that when these switches are in the normal or N position energization of a TD relay effecting closure of the corresponding TD2 contacts will apply D.C. voltage through conductor 114 to the SW terminals of the spare inverter.

The TD relays 32TD, 50TD, 68TD and 86TD also have correspondingly numbered contacts TD3. The contacts 32TD3 are connected in the ground return conductor 160 for all three relay coils 102TR, 104TR and 106TR. The contacts 50TD3 are interposed in the ground return conductor 162, connected to conductor 160, for the two relay coils 104TR and 106TR; and contacts 68TD3 are similarly interposed in the ground return conductor 164, connected to the conductor 152, for the single relay coil 106TR. Normally these contacts are closed. These TD3 contacts and their connections as described produce the desired priority sequence operation of the system as will be pointed out subsequently in greater detail.

The TD relays 32TD, 50TD, 68TD and 86TD also `have. correspondingly numbered contacts TD4 and these normally closed contacts are interposed in the circuit conductors which carry D.C. voltage from the contacts N of the leftmost switch arms 20L, 46L, 64L and 82L of the respective switches bearing corresponding identifying numbers, to the rightmost contact N of the respective switch arms 20R, 46R, 64R and 82K, furnishing a current path for normal energization of the associated inverters,

The operation of the described circuits by which any of the four inverters, 10, 12, 14 or 16, is automatically replaced by the spare inverter in the event of an overvoltage or under-voltage condition of the impaired section of the system is basically the same in each instance, and it will be sufficient for that reason to describe the operation of substituting the spare inverter for the main inverter 10 under these conditions.

Assuming an over-voltage condition which persists long enough to charge the condenser across the coil of relay 7 MQOV' and: actuate thatfre'lay, the relay'contacts:152937911v will-.f close. and. relay coil 98TR' willb'esenergized thlough' conductors .3d and lllxthus connectedzzinrseries. Sucht` action.` reverses the :existing positions ofv the--relay contacts.; 9STRi. and 98TR2 in order to switch;theespareV inner-tori feed conductor 198 tothe bus: 90h11. placeofthe normal (.unnurnhered) feed conductor-.from `the main-inverter 10:;

/ At thesame time, thesparetinyerter isfenergized-aby.clo-V sure` ofthe contacts 32TD2,.establishing:anrinverten ener-f gizing circuit through the-.switcharmlGM yanda conductor: 114; When. contacts: lSZOVl cl'osed in'. order. 'tozenergizecf relay coil QSTR they simultaneously energized relaycoili 323213, because; thertwo coils. arer connected. inparallel; Thus, the spare: inverter.'v 1-82 is: energized; through-.contacts 32l'3D2-A at: virtually the. saine: instant that` the spare.in verter feed. conductor lilSfis switched to: the bus:9il.=.fin. place. of themain inverter feed conductor.utormerly'ex tending through. contacts SSTRZ'; Thusapersistenu overvoltage condition: which actuates. the`y over-voltage relay leiiOV automatically substitutes .the spare inverter for the=main inverter 10 supplyingfthe .bus 90':

Thewspare inverter may be removed from the mainv inverter bus thereafter by moving the switch 2? out of= its:,,N positionrtofa yneutral position, .causing de'energi'zationaof, relay SZTD. and: thereby of: .relay-98TH; wherebyA the.. latters contacts reversey position; Thereupon the switch 2tirnay be moved to the S."positio'n.tosubstitute the spare manually for. the-main inverter, or the switch Ztlfmay. be movedback tothe l"N position. If. thelatter is. done one oftwo results-is possible, eitherfthe main in-l verter will operate normally, with.its1 fault corrected, or. else the former over-voltagecondition:.will: stilleXistand' the spare inverter will again be substituted? for it auto-1 maticallyin themannerpreviously;described;

In case. of an under-voltage-condition on the-bus 901 causing the under-voltage reIayxlSZUV todrOp-out; and thereby close its contacts 132U\Ll'-,.heatingv current ows. ingtheheating element. 1'50H; A certain periodici time is` required. for. heating the element ltlH. to a temperature sufiicientl to actuate and close the:v associated contacts M-I1, thus allowing time for: the under-voltage.conditionz to correct itself', if it will, .beforefthere is. aresponse causingchange-.over of inverters. This ;delayfis4 desirable,y as therev are variousreasons in-the--operationiof an'elec trical system of this naturezwhy an under-voltage (or. no. voltage) conditiommayexist for*y afbrief. instant without itsgbeing caused by a failure.v

When contacts l'tlHd do close, theyf form an energizing circuitafor both-relays 32TD1and398TR', with'the' eectspreviously. described: with -referencetto a main in verter over-voltage condition, namely'the ,energization' ofI thetspare inverter, 18.and=theswitching-of itsiteed.V conductortlt to the'bus Qilzinplaceof thefnormalfeed conductor from the main inverter't): Inaddition, however, energization of the relay SZTDS causes opening` ofthe contacts BZTDKJJ` and.y thereby.n removes .-thesource of.` voltage causing heating of the, element. 15M-I', so'asA to avoid proionged'heatingfperiodsaof the'latter tendingfto produce deteriorationl thereof. The'coutacts-,1SOH then reopen',- but this does not. deenergizeitherelayS'SQ'ITDand 9STR', however,l becausethe relay SZTDisazholding; relay. provided with,l contacts SZTD', ,in parallel? withv the contacts lStlH-l.; As in the; casezof: anovervoltage=.condition; the' substitution ofthe sparezinverterfor: the main inverter due to under-voltage on bus 90 is in eiect a permanent* subi stitution, y,whichgremains ,until ithe .switchZtlis moved out of its N position to .the neutral'position.-

Whenthe secondary; inverter I6.is .substituted byfman ual control'for the main -inverter l0; thenopening of contacts ltltiSMS attending the .switchingv operation. neces.

sarily removes voltage from.thexsecondaryy inverter vbusn 96.. This removal of, voltage from the-busis,ofcourse7 the equivalent ofl an undenvoltage condition during normal operation off the secondary inverter-when.connectedto that bus. Consequently, the under-voltagev relay 138UV4 responds as if to A anunder-voltage'condition, and causes actuation ofY the relays 86TH and ltlTR `so as` to, eHect substitution of thefsparev inverter i8 fon the. secondary inverter as asource of energyffor. the; busz96'.. Thus the spare inverter automaticallymoves-upto the po-y sition of the secondary inverter ldd/henthe-latter. isv moved upby manual switching operationlswitchzllst position S) to the positiornot. themain-.inverterr 10,; Howevenbecause of thepriorityasequence connections in the system, .as laterV describechthefspare-:inverterfisistill ayailableifto:substitutefon ther-Norl o1r5No.g2 camera-.ine verter. the spare moves upir totits placeyitwill'` usuall'ywbefdesir-ableto open switch'Ztl. (i. ecmovexit* to a neutral posi` tion.) and disconnect thespare inverter -frombus 90, while.- movingrswitch. 22; tot the, .S" positionA and: thereby sub.A stitnte the secondary' 'inverter in place .ofy the. spare inverter as asupply for'mainbusil. Thesparethen autof maticallyxbecomes. connectedrto. the secondary bus 96;;

While the'secondary inverterfl may bet replacedy auto.. matically by the spare inverter: 18 'when the secondary. inverter. is; disconnected fromt its'. own'. bus 96 by. opening: oi theinorrnal'ly closedzcontacts 1.06TR2" and 100S'M1,:the, spare will not'- substitute for the main4 inverter^while the.

. secondary is connected'to. the main. inverter bus.` 90by' In order to: furnish-over-voltage` protectiony forthesec-v4 ondaryv inverten when. the latter is. di'sconnectedfromfitsf own-.bus-.96z and? associated'over-voltage protection oon-- trois.,.andiis connected to-the mainv inverter bus9il, a sepa rate.overvoltage responsive circuit is lconnectedjtothe outputfof the secondary inverter through the conductor li66v This separate yover-voltage*responsivev circuit` com` prises. the bridge-connected rectifier 16senergizingl theover-voltagerelay 170; havinga condenserv C connected across itsl winding and a variable resistor connected inl series with itsl windingin order to establish the critical'I actuating voltage ofthis relay. This over-voltagek relay has aset: of contacts 1'70OV1 which are normally open,V4 and whenclosed by an over-voltagey condition; at the out.-l

put yoflthe. secondary inverter elect energization of the' relay 172SE' from the conductor 120,'.which in'turnA is'4 energized through switch arm -22Rvwhen1 'the secondary inverter isswitchedmanuallylintofthe position of substi tuting for the main inverter.` Relay l7ZSE isa holdingy relay having contacts 17251515 connected in parallel with thev-over-voltagerelay contacts IitlOV'l.`v A secondset* of contacts172SE2 of the holding relayare interposedin theconductor which energizes-the secondary inverter, and these normally closed contacts are openedwhcnan over-voltage condition exists on conductor-166 causing, the over-voltage OV' to beactuated., Anullifying switch 174connected across the relay contacts l72SE2` is provided for the purpose'v-ofirestoringthe secondaryin.- verter.- to operating conditiongdespritel an overvoltage. conditionat its output, and this would he' done` inthe event of t an emergency when the secondary jinverter is essential,y even though operating with excessive output'voltage.:`

Thesarne type of separate, over-voltage control for: thel spare-inverter is provided byjthe bridge-connected rectifier: 176,' overvoltagerelay li'SOV having contacts, USOVI,` and the holdingj relay lliSP havingY contacts; litlSPl connectedxin.paralleli with theV contacts 178OV1. A. separate set ofcontacts' IStlSPZYinterposed inthe. en: ergizatio'n conductor llftf'of'V the spare inverter removes the energizing voltage `from thisl inverter when an oven, voltage condition-exists at its output, as in the case of. the secondary inverteroverevoltagecontroloperation. A nullifyingy switch 182". connected' across the contacts.. liiilSlJZ 'i's provided in the event it is desirable incaseof; emergency to-removethe over-voltage protection provided'.V tothe spareinverter:

Reierencevhas been made tol the presence. ofTDzrel'ayv Contacts serias; sarna-'amivssrDsin the., gmundgre.- turn conductors for the various TR relays. These relay contactsl have thepurpose ofv insuring 'thatthe spareinrverter will be substituted' automatically forthe failed in:- verterot highestpriority; should. therehe two orffmore. normally operative inverters under failure at=the,.san1e; time andf both requiringreplacement. Thesecontacts and their lcircuit connections also insurethata person may` substitutethel spare inverter, for any -,inver.ter` of'higher: priority thanthat', if any, for. which ther spare had'jalreadyy been` substituted, whether `manuallyjor automatically.. This: the operator accomplishes by moving thegang switch.

. of the desired high priority inverterfto position S."" The operation-.ofthe TDSy contacts tol achieve' thoseends willnovi/.bef described.;

It a will;y bennoted:r rstt of all that the substitution' of Athel sparefinverter -for the-=maih"inverier., for` example;` is'v eieeted,1.amongother things; by energization `:of-the' relay' For that reason, if the main inveriter'dails:` and;

32TD. Thus when this substitution is made the relay contacts 32TD3 are opened. This opens the common ground return conductor 160 vfor the relays 102TR, 104TR and 106TR associated, respectively, with the No. l and No. 2 camera inverters and the secondary inverter. Thus while the spare inverter is substituting for the main inverter, it is impossible for any of these latter three relays to be energized by operation of the automatic over-voltage and under-voltage controls of their associated circuit sec tions. This is as it should be, of course, because the main inverter has the highest priority of all.

Should the No. l camera inverter, for example, fail before the main inverter fails, so as to cause automatic substitution of the spare inverter for the No. 1 camera inverter, then the attending opening of the contacts 50TD3 in ground return conductor 162 for the relay coils 104TR and 106TR interrupts the ground return lead for these relays and prevents failure of the No. 2 camera inverter or the secondary inverter from disturbing the connections of the spare inverter to the No. l camera inverter bus 92. However, should the main inverter suffer a fault while the spare is substituting for the No. 1 camera inverter, operation of the under-voltage relay 132UV or the overvoltage relay 140OV will energize relay 32TD. Contacts 32TD1 are thereby closed to energize relay 98TR, which connects the spare inverter feed conductor to the bus 90. Simultaneously therewith contacts 32TD3 open, thus breaking the energizing circuit conductor 160 for relay 102TR. With relay 102TR deenergized, contacts 102TR1 open and disconnect the No. 1 camera inverter from the bus 92, leaving the spare inverter 18 connected only to the main bus 90. Thus failure of the main inverter, automatically causes the spare to move up to its position from the lower priority position of the No. l camera inverter.

By similar action, if the spare inverter is substituting Y for the secondary inverter, and there is a failure of any one of the higher priority inverters 10, 12 or 14 the spare will move up automatically to take its place. Likewise if the spare inverter is substituting for the No. 2 camera inverter, then only a failure of the main inverter or the No. l camera inverter can draw the spare inverter to their respective busses, and failure of the lower priority secondary inverter will not disturb the spare inverters connection to the No. 2 camera bus 94.

As manual substitution of the spare for any other inverter requires energization of the appropriate TR relay, effected by moving the corresponding switch 20, 46, 64 or 82 to the S position, the TDS contacts insure, as in the case of automatic operation described above, that the spare inverter may always be substituted manually for one inverter in preference to all others of lower priority in the system.

There is thereby provided a priority change-over system wherein failure in one section of the system actuates a disabling switch individual to it and thereby prevents the connection of the spare inverter to any lower priority section without preventing its substitution for one of higher priority.

Having thus described the invention relating to transfer systems with reference to the preferred form, it will be appreciated that a number of equivalent arrangements as well as modifications or changes in the existing arrangement may be made without departing from the underlying features comprising the patentable subject matter, as defined in the appended claims.

l claim as my invention:

l. A transfer priority electrical distribution system comprising a plurality of normally operative power supply units operatively connected in associated sections of circuit apparatus individual to said units respectively, said apparatus sections having a predetermined order of priority for connection to a spare power supply unit, a spare power supply unit normally inoperative adapted to substitute for any of said normally operative units, a plurality of transfer relays individual to the respective apparatus sections and each controlled by its section and arranged to substitute said spare unit for the unit associated with such relay automatically in response to an abnormal voltage condition of the related apparatus section, and disabling switch means controlled by the high priority apparatus section to prevent spare unit substituting operation of the transfer relays of lower priority sections, automatically substantially concurrently with the operation of said high priority section transfer relay.

2. The system defined in claim l, wherein the transfer relays of the lower priority sections have separate energizing circuits for such relays but include a common conductor for the energizing currents of all such relays, and the switch means is interposed in said conductor to interrrupt or prevent flow of energizing current in any such relay upon operation of such switch means concurrently with the operation of the higher priority section transfer relay.

3. The system defined in claim 1, and manually controlled transfer switch means including a normally closed switch in the operating connections between the high priority section power supply unit and its associated apparatus section, circuit connections and a related normally open switch between the high priority section and a lower priority section power supply unit, and a switch in the operating connections between said lower priority section unit and its associated apparatus section, operation of said switch means disconnecting said units from their respective sections and substantially simultaneously substituting said lower priority section unit for said high priority section unit, whereby the transfer relay of said low priority section automatically substitutes the spare unit in such latter section in response to the removal of normal voltage for such section.

4. The system defined in claim l, comprising at least three apparatus sections and associated normally operative power supply units, said sections having a successive order of priority, with the disabling switch means being controlled by the highest priority apparatus section of the three and operating to prevent operation of the remaining two apparatus section transfer relays, and a second disabling switch means controlled by the intermediate priority apparatus section of the three and arranged to prevent operation only of the transfer relay of the lowest priority apparatus section of the three.

5. The system defined in claim 4, wherein the trans fer relays of the intermediate and lowest priority sections of the three have separate energizing circuits for such relays but include a common conductor for the energizing currents of both such relays, and the first disabling switch means is interposed in such common conductor to permit interrupting or preventing flow of energizing current in either such relay, while the second disabling switch means is interposed in a portion of the separate energizing circuit for said lowest priority section relay removed from said common conductor, to interrupt or prevent iiow of enlergizing current in the transfer relay of such latter re ay.

6. The system defined in claim 4, and manually controlled transfer switch means including a normally closed switch in the operating connections between the highest priority section power supply unit and its associated apparatus section, circuit connections and a related normally open switch between the highest priority section and the lowest priority section power supply unit, and a switch in the operating connections between said lowest priority section unit and its associated apparatus section, operation of said switch means disconnecting said units from their respective sections and substantially simultaneously substituting said lowest priority section unit for said highest priority section unit, whereby the transfer relay of said lowest priority section automatically substitutes the spare unit in such latter section in response to the removal of normal voltage from such section.

7. A transfer priority electrical system comprising a plurality of normally operative units operatively connected in associated sections of circuit apparatus individual to said units respectively, said apparatus sections having a predetermined order of priority for connection to a spare unit, a spare unit normally inoperative adapted to substitute for any of said normally operative units, a plurality of transfer relays individual to the respective apparatus sections and each controlled by its section and arranged to substitute said spare unit for the unit associated with such relay automatically in response to a predetermined abnormal operating condition of the related apparatus section, and switch means controlled by the high priority apparatus section and controlling the transfer relays of lower priority sections, said switch means being operable substantially simultaneously with the operation of said high priority section transfer relay, and thereupon preventing operation of said lower priority section transfer relays, thereby preventing substitution of said spare unit for any of said lower priority section units 11`1 `.when said; higherprioritysection .unit requiressuchsubstitution.

8. A transfer priority system-comprising a pluralityof .normally .operative .units operatively connected in `as- Vsociatedsections .of apparatusindividual to said units respectively, vsaid apparatus sections having a predeter- `mined order of priorityfor connection to a spare unit, a .spareunit normally inoperative adapted to substitute for any of said normally operative units, a plurality of transfer devices individual to the respective apparatus sections ,and each controlled by its section and arranged .to substitutesaidspareunit for the unit associated with such-device automatically in response to a predetermined .abnormal operating condition of the related apparatus section, and disabling means controlled by the high priority apparatus section yand arranged to prevent substitution of said spare unit for lower .priority sections by operation of the transfer :devices of such .latter sections, said disabling means being operable with the operation'of said high priority section transfer device.

`9. The system defined in claim 8, comprising at least .three apparatus sections and associated normally operative units, said sections having a successive vorder of priority, with the means being controlled by the highest priority apparatus section of the three and operating to prevent operation of the remaining two apparatus sec- :tion transfer devices, and a second .disabling vmeans con- :trolled by the intermediate priority apparatus lsection of the three and arranged to prevent operation only of the transfer device of the lowest priority apparatus section of the three.

l0. An electrical distribution system comprising a plurality of feeder busses supplied respectively by separate inverters normally connected thereto, a spare inverter adapted to substitute for any of said normal inverters, a plurality of transfer relays operable to sub` stitute said spare for said normal inverters, respectively, automatic relay .energizing means controlling the relays ,associated with said normal inverters respectively and ycontrolled in turn by voltage of the busses yof such Vinverters to effect energization of such relays Aindividually and thereby substitute the spare inverter for any of such latter inverters automatically in response to an abnormal voltage conditi-on on its bus, .and switch means operable by manual control to substitute one of said .normal inverters for a'particular one thereof.

11. The system ldefined in claim 10, and disabling means operable to prevent actuation of the :respective transfer relays of all of the normal inverters except that of the particular inverter last mentioned, said disabling means being arranged to operate automaticallywith substitution of the spare inverter for said particular inverter, and thereby give precedence thereto.

12. The system defined in claim l0, vcomprising at least three busses and associated normal inverters, said ,busses Vhaving :a successive order of priority for connection to the spare inverter, with the particular inverter last mentioned being highest, rst disabling means operable to prevent actuation of the respective transfer relays of the other two normal inverters and `being arranged to operate automatically with substitution vof the spare inverter for said highest priority bus inverter, a second disabling means operable to prevent acuation yof the transfer relay of the lowest priority bus vof the three and being .arranged to operate automatically with substitution of the spare inverter for the intermediate priority inverter of the three.

13. An electrical distribution system comprising a'plurality of distribution busses, a plurality of independent power supplies individual to the respective busses and normally connected thereto, a spare power supply adapted to substitute for any of said normally connected power supplies, said busses having a successive order of priority for connection to the spare power supply, a plurality of multiple contact transfer relays associated with the respective busses and operable to disconnect any such bus from its normal power supply and to said spare power supply, a plurality of voitage sensitive devices individual to the respective busses, controlling energiza.-

tion of the related transfer relays to effect actuation of any such relay automatically in response to an abnormal voltage condition on its related bus, and thereby substitute the spare power supply Yfor that normally connected to such related bus, said system additionally including disabling means associated with the respective inmeans of its particular bus and ybeing arranged and op- .erable toprevent substitution of the spare power supply for that -of any-other bus of llowerpriority than that of the bus associated with the particular disabling means.

14. The system defined in claim 13, wherein the disabling means. comprise .switches interposed in lthe control circuits of the respective .transfer relays.

15. The system defined in claim 14, wherein the energizing circuit of each transfer relay, except that associated with the highest ypriority bus, has .a circuit conductor in common with the energizing circuits only of those respective relays associated with all lower priority busses, -and the `disabling switch associated with each bus is interposedin said relay energizing circuit conductor of the bus of next lower priority.

1.6. The system `defined `in claim 15, and separately controlled switch means arranged for disconnecting the normal power supply of abus andsubstituting said power supply for the power supply-of -a bus of higher priority, thereby removing voltage fromsaid first bus and effecting operation of vthe related transfer relay to substitute the spare power automatically for the power supply of such first ybus. Y

17. The system definedxin claim 1.3, and separately controlled switch means arranged for disconnecting the normalpowersupply of abus and substituting said power supply for the power supply of a bus of higher priority, thereby removing voltage from said first busand effecting operation of the related transfer relay to substitute the spare power supply ,automatically for the power supply -of such .first bus.

18. A system of electric energy distribution comprising a plurality of busses, a plurality of inverters located remotely from said ybusses and normally connected to the respective busses over normal feed conductors extending lfrom such linverters to suchbusses, and a spare Vinverter having a feed conductor extending therefrom to veach `bus but normallydisconnected therefrom, a plurality of transfer relays for the respective busses and physically located at the inverter ends of their associated normal feed conductors, said relays each having a set of normally closed contacts connecting the associated bus tothe normal inverter feed conductor and a set of ,normally open contacts connecting such bus to the spare inverter feed conductor, and voltage sensitive means respectively associated with the individual busses and controlled by the respective voltages thereof, said means in turn controlling the associated transfer relays to actuate such relays automatically in response to abnormal bus voltage and thereby substitute said spare inverter for the particular bus inverter of an abnormally energized bus.

19. The system defined in claim 18, wherein the busses have a successive order of priority for connection to the spare inverter, and one of the inverters normally connected to a bus ofrelatively low priority has an additional feed conductor extending therefrom to the physical location of a bus of relatively high priority, and remotely controlled switch means having normally open contacts interposed between said additional feed conductor and said relatively high priority bus. and having additional contacts coordinated therewith at said relatively low priority inverter, operable tc effect substitution of such inverter for said relatively high priority inverter.

20. The system defined in claim 19, wherein the busses have a successive order of priority for connection to the spare inverter, such system being additionally characterized by the provision of disabling means associated with the respective individual busses, except the bus of lowest priority, each of said disabling means being controlled by the voltage sensitive means of its particular bus and being arranged and operable to prevent substitution of the spare inverter for that of any other bus of lower priority than that of the bus associated with the particular disabling means.

21. The system defined in claim 20, wherein the disabling means comprise switches interposed in the control circuits of the respective transfer relays.

22. The system defined in claim 2l, wherein the energizing circuit of each transfer relay, except that associated with the highest priority bus, has a circuit conductor in .Common with the energizing circuits only of those respective relays associated with all lower priority busses, and the disabling switch associated with each bus is interposed in said energizing circuit conductor of the bus of next lower priority.

23. The system defined in claim 20, and manually controlled means respectively associated with the individual normally operative inverters and arranged to effect actuation of their related transfer relays selectively and thereby substitute the spare inverter for any such normally operative inverter at will.

24. The system dened in claim 18, and manually controlled means respectively associated with the individual normally operative inverters and arranged to eiect actuation of their related transfer relays selectively and thereby substitute the spare inverter for any such normally operative inverter at will.

25. An electrical distribution system comprising a plurality of distribution busses, a plurality of independent power supplies individual to the respective busses and normally connected thereto, a spare power supply adapted to substitute for any of said normally connected power supplies, a plurality of multiple contact transfer relays associated with the respective busses and operable to disconnect any such bus from its normal power supply and to said spare power supply, a plurality of voltage sensitive devices individual to the respective busses, controlling energization of the related transfer relays to effect actuation of any such relay automatically in response to an abnormal voltage condition on its related bus, and thereby substitute the spare power supply for that normally connected to such related bus, and a plurality of manually controlled means individual to the respective busses, controlling energization of the related transfer relays to eect actuation of any such relay and thereby substitute the spare power supply for that normally connected to such related bus at will.

Number Name Date Wallace et al. June 1, 1948 

